Power supply device for plasma processing

ABSTRACT

A power supply device for plasma processing, wherein electric arcs may occur, comprises a power supply circuit for generating a voltage across output terminals, and a first switch connected between the power supply circuit and one of the output terminals. According to a first aspect the power supply device comprises a recovery energy circuit connected to the output terminals and to the power supply circuit. According to a second aspect the power supply device comprises an inductance circuit including an inductor and a second switch connected parallel to the inductor. According to a third aspect the power supply device comprises a controller for causing the power supply circuit and the first switch to be switched on and off. The controller is configured to determine a quenching time interval by means of a self-adaptive process. The quenching time interval defines the time interval during which, in an event of an arc, no voltage is generated across the output terminals.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a continuation of U.S. patent application Ser. No. 12/701,813,filed Feb. 8, 2010, which claims the foreign priority of European PatentApplication No. 09405031.7, filed Feb. 17, 2009 in the names of AlbertBULLIARD, Benoit FRAGNIERE, Joel OEHEN, and Olivier CARDOU and entitledA POWER SUPPLY DEVICE FOR PLASMA PROCESSING, the disclosures of whichare incorporated by reference herein.

FIELD OF THE INVENTION

The invention concerns a power supply device for plasma processing.

BACKGROUND OF THE INVENTION

There are variety of processes in which a plasma is generated to depositand/or to remove material. Examples are the process of sputtering, wherematerial is removed from a target and deposited on a substrate in orderto produce e.g. a thin film, or the process of etching, where atoms areremoved in order to create e.g. a very clean surface.

To produce the plasma, a high voltage is generated between electrodes bymeans of a suitable power supply device. However, the processingconditions may be such that there is a sudden electrical discharge forinstance between the electrodes which causes the occurrence of one ormore arcs. Normally, such arc events are to be prevented since they maylead e.g. to damages in the target or to a poor quality of the surfaceto be processed.

It is widely known to use a switch for interrupting the power supply tothe electrodes when an arc event occurs (see e.g. U.S. Pat. No.5,192,894 or U.S. Pat. No. 6,621,674 B1). However, interruption of thepower supply gives rise to the problem that the energy which is storede.g. in the cables at the time of interruption is supplied to theplasma, which may impede a quick quenching of the arc. Eventually, theduration until the plasma processing is in an arc-free condition andoperates normally may be prolonged.

The patent application US 2004/124077 A1 refers to a power supply whichis suitable in the field of so-called HiPIMS (“High Power ImpulseMagnetron Sputtering”). The power supply, which produces very shortpulses of extremely high power, is provided with a capacitor that isrepetitively charged and then discharged through an inductor. When anarc is detected, the capacitor is first disconnected from the inductorby actuating a first switch and then connected to the inductor again byactuating two other switches such that the energy contained in theinductor is recycled to the capacitor. Compared to this recycled energy,the energy contained in any cables connecting the output terminals ofthe power supply with the plasma processing chamber is negligible. Thus,no measures are provided to recover this energy in the cables.

In the patent application US 2008/309402 A1, it is proposed to use apre-charging/discharging circuit for pre-charging a capacitor undernormal operating conditions. When an arc is detected, an amount of theresidual energy which is stored in the cables leading to the plasmaprocessing chamber is transferred into the capacitor and finallyeliminated by means of the pre-charging/discharging circuit before thepower is applied again to the plasma processing chamber. Thus, theenergy is finally lost, which makes the operation inefficient.

Apart from the problem of the energy in the cables, another problemimpeding an efficient handling of arcs may arise when the time ofinterruption of the power supply is not optimal, e.g. the time is tooshort to quench an arc.

In the patent U.S. Pat. No. 6,621,674 B1, it is proposed to adjust thetime interval during which the voltage is applied to the electrodes inan adaptive manner, whereas the time interval during which the voltageis disconnected is kept constant.

SUMMARY OF THE INVENTION

One object of the present invention is to provide a power supply devicefor plasma processing which allows the handling of arc events in a moreefficient way.

According to a first aspect of the invention this object is achievedwith a power supply device comprising a recovery energy circuit forfeeding at least partially the energy back which is stored in theconductors when the power supply to the plasma processing chamber isinterrupted. The power supply circuit is configured to reuse the energyfed back at least partially for the power supplied to the plasmaprocessing chamber.

According to a second aspect of the invention there is provided a powersupply device comprising a first switch and an inductance circuit thatcomprises an inductor and a second switch. The first switch is arrangedoutside of the inductance circuit and the second switch is connectedparallel to the inductor.

According to a third aspect of the invention there is provided a powersupply device comprising a controller being configured to determine aquenching time interval by means of a self-adaptive process. Thequenching time interval defines the time interval during which, in anevent of an arc, no voltage is generated across the output terminals ofthe power supply device.

Each of the three aspects has the advantage that arcs which occur in theplasma processing chamber can be handled in a more efficient way.

BRIEF DESCRIPTION OF THE DRAWINGS

The subject invention will now be described in terms of its preferredembodiments. These embodiments are set forth to aid the understanding ofthe invention, but are not to be construed as limiting.

FIG. 1 shows an embodiment of a plasma processing installation includinga power supply device according to the invention,

FIGS. 2 to 5 show various embodiments of the inductance circuit of thepower supply device of FIG. 1,

FIG. 6 shows an alternative embodiment of the energy recovery circuit ofthe power supply device of FIG. 1,

FIG. 7 shows the temporal development of U, I and I₂₂, where U is thevoltage between the electrodes, I the current passing through theelectrodes, and I₂₂ the current passing through the branch parallel tothe inductor of the power supply device of FIG. 1,

FIG. 8 shows schematically the state of the installation of FIG. 1 in afirst time interval t₀-t₂,

FIG. 9 shows schematically the state of the installation of FIG. 1 in asecond time interval t₂-t₄,

FIG. 10 shows schematically the state of the installation of FIG. 1 in athird time interval t₄-t₅,

FIG. 11 shows schematically the state of the installation of FIG. 1 in afourth time interval t₇-t₉,

FIG. 12 shows a first example of the temporal development of |U|(absolute value of the voltage between the electrodes) and of I (currentpassing through the electrodes) for the case that the plasma recoversafter one arc event only,

FIG. 13 shows a second example of the temporal development of |U| and ofI, and

FIG. 14 shows a third example of the temporal development of |U| and ofI as well as the corresponding switching states of the power supplycircuit and the serial switch of the power supply device of FIG. 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows a plasma processing installation including a power supplydevice having output terminals 1 and 2, which are connected to a plasmaprocessing chamber 7 by means of a pair of wires 3, 4 forming e.g. acable. The output terminals 1, 2 are normally located outside of thehousing of the power supply. The processing chamber 7 is designed toproduce a plasma therein for accomplishing the desired process such asdeposition or etching of a material. Electrodes 5 and 6 are located atthe end of the wires 3, 4. The negative electrode 5 (“cathode”) isconnected to a target 8 located inside the processing chamber 7. Thepositive electrode 6 (“anode”) is connected e.g. to the housing of theprocessing chamber 7 or to an internal electrode. During the processingoperation a voltage U is developed across the electrodes 5 and 6. As thecase may be, there is also a substrate (not shown) located inside theprocessing chamber 7.

The power supply device comprises a power supply circuit 10 to produce aDC voltage across the terminals 16 and 17. In the embodiment shown inFIG. 1 the power supply circuit 10 comprises an AC input 11, which ise.g. connected to the power supply network, a first rectifier 12, aswitching circuit 13, a transformer 14 and a second rectifier 15. Theswitching circuit 13 includes e.g. a H-bridge with switches which arecontrolled by a controller 60.

The first terminal 16 of the power supply circuit 10 is connected via aninductor 21 and a serial switch 25 to the negative output terminal 1.The switch 25 is e.g. a transistor such as an IGBT and is controlled bythe controller 60.

The second terminal 17 is connected to the positive output terminal 2and via a capacitor 27 to the first terminal 16. The inductor 21 limitsthe temporal variation of the current, dI/dt, during an arc event (seethe moderate slope of curve 71 in FIG. 7 in the time interval t₁-t₂).The capacitor 27 serves for storing energy.

A switch 22 is arranged parallel to the inductor 21. The switch 22 ise.g. a transistor, such as an IGBT or a power MOSFET and is controlledby the controller 60.

FIG. 2 shows an example of a switch 22 being composed of a power MOSFET2T having a serial diode 23, which serves as a freewheeling diode.

In case that the switch 22 is an IGBT 22″ as shown in FIGS. 3 to 5,there is preferably provided an overvoltage protection in form of acomponent which is connected parallel to the switch 22. This componentmay be e.g. a voltage suppressor, such as a Zener diode 24 as shown inFIG. 3 or a TVSS (Transient Voltage Surge Suppressor) 24′ as shown inFIG. 4, a power resistor 24″ as shown in FIG. 5, or any other suitablemeans for protecting the switch 22 against an overvoltage.

In case that the switch 22 is an avalanche rated power MOSFET, it has aninherent overvoltage protection.

An overvoltage may e.g. occur in the case that the plasma does notre-ignite after the switch 25 has been closed again and the switch 22 isopening after an arc event, so that the voltage across the inductor 21is increased, or in the case that—due to a malfunction—the switch 25 isopening when the switch 22 is opened.

In the embodiment shown in FIG. 1, the components 21, 22 form aninductance circuit 20 which is arranged between the terminals 16 and 1and is thus integrated in the negative branch of the circuit.Alternatively, the inductance circuit 20 can be integrated in thepositive branch by arranging it between the terminals 17 and 2 or it isconceivable to provide each branch with an inductance circuit 20.

The power supply device shown in FIG. 1 further comprises a plasmafloating potential neutralizing circuit 30 (in the following denoted by“PFPN circuit”) connected to the negative terminal 1 and the positiveterminal 2 and an energy recovery circuit 40 arranged between the outputterminals 1, 2 and the power supply circuit 10.

The PFPN circuit 30 comprises a diode 31 and a switch 32. The switch 32is e.g. a transistor such as an IGBT and is controlled by the controller60.

The energy recovery circuit 40 comprises a first line 41 which connectsthe negative output terminal 1 via a diode 45 to the primary winding 46a of a transformer 46, a second line 42 which connects the positiveoutput terminal 2 to the primary winding 46 a of the transformer 46, athird line 43 which connects the secondary winding 46 b of thetransformer 46 via a diode 47 to a first input terminal 18 of the powersupply circuit 10, and a fourth line 44 which connects the secondarywinding 46 b of the transformer 46 to a second input terminal 19 of thepower supply circuit 10.

The power supply circuit 10 comprises a capacitor 9, which is connectedto the first input terminal 18 and the second input terminal 19. Thus,the power supply circuit 10 is suitable to reuse the energy which is fedback via the energy recovery circuit 40 at least partially for the powersupplied to the plasma processing chamber 7.

In an alternative embodiment the energy recovery circuit 40′ is designedas shown in FIG. 6 by providing a DC-DC converter 48 whose input isconnected to the lines 41, 42 and whose output is connected to the lines43, 44, and a capacitor 49 which is connected to the input of the DC-DCconverter 48.

The power supply device shown in FIG. 1 further comprises an arcdetection circuit 61 for detecting the occurrence of an arc conditionand for generating an arc detection signal which is processed by thecontroller 60. The arc detection circuit 61 measures e.g. the currentthrough the negative or positive branch and the voltage across the twooutput terminals 1, 2.

In the following the operation of the power device is explained in moredetail. In the event that an arc occurs, the controller 60 controls theswitches 22, 25, and 32 to activate the circuits 20, 30, and 40 suchthat the arc is suppressed and/or quenched and the normal operation modeis recovered in an efficient way.

In the following, successive instances of time t are referred to as t₀,t₁, t₂, etc. The following table summarizes the successive states of theswitches 22, 25, and 32, where “OFF” means that the switch is open and“ON” means that the switch is closed. For some of time intervals theswitches 22 and 32 may be either ON or OFF (denoted in the table by“or”). In case of transistors, a switch 22, 25, or 32 is “ON”, when itis in the conducting state, and “OFF”, when it is in the non-conductingstate.

switch 32 of time interval switch 22 of circuit 20 serial switch 25circuit 30 t₀-t₁ ON or OFF ON OFF t₁-t₂ ON or OFF ON OFF t₂-t₃ ON OFFOFF t₃-t₄ ON OFF OFF or ON t₄-t₅ ON OFF ON t₅-t₆ ON OFF OFF t₆-t₇ ON ONOFF t₇-t₈ OFF ON OFF t₈-t₉ OFF ON OFF t₉-t₁₀ ON or OFF ON OFF

By actuating the switches 22, 25, 32, the voltage U between the target 8and the positive electrode 6 and the current I passing through theelectrodes 5 and 6 change in time.

FIG. 7 shows an example of the temporal development of the voltage U(solid curve 70) and the temporal development of the current I (solidcurve 71), when an arc event occurs. The dotted line 72 indicates thetemporal development of the current I₂₂ flowing through the parallelbranch 22 of the inductance circuit 20.

At time to the plasma processing is in the normal operation mode, wherematerial in the processing chamber 7 is deposited or etched according tothe setup of the plasma processing installation. The voltage U has avalue which is in the present example negative. The switch 22 is open orclosed, the switch 32 is open, and the switch 25 is closed. Thus, thereis a current flowing from the terminal 17 through the wire 4 and theplasma in the processing chamber 7 back to the terminal 16 via the wire3. This is schematically shown in FIG. 8, where the direction of thiscurrent is indicated by the arrows 80.

At time t₁ an electric arc occurs in the processing chamber 7, which hasthe effect that the voltage U tends to zero, whereas the current Iincreases (see the curves 70 and 71 between the two instants of time t₁and t₂ in FIG. 7). The inductor 21 limits the temporal variation of I,so that the slope dI/dt is moderate. The change of voltage, U0, may bee.g. in the range of several tens V to several hundreds V.

At time t₂ the arc detection circuit 61 detects the arc occurrence inthe processing chamber 7 and produces an arc detection signal causingthe controller 60 to close the switch 22 and to open the switch 25. Theenergy in the wires 3, 4 at the time t₂ is approximately given byL_(c)·I²/2, where L_(c) is the inductance of the wires 3, 4. The currentoriginating from the energy in the wires 3, 4 begins to flow via theenergy recovery circuit 40 to the power supply circuit 10, where it isstored in the capacitor 9. This is schematically shown in FIG. 9, wherethe direction of this current is indicated by the arrows 81. At the sametime the current stored in the inductor 21 flows through the switch 22as indicated by arrows 82 in FIG. 9.

Referring back to FIG. 7, it can be seen that at time t₂ the voltage Uchanges its polarity and reaches a certain level U_(Lc) due to theenergy in the wires 3, 4. The level U_(Lc) corresponds to the voltagebetween the lines 41 and 42 and defines the decay time τ of the currentI, which is given by τ=L_(c)·I/U_(Lc).

As can be seen from FIG. 7, the voltage U remains substantially at thelevel U_(Lc) in the time interval t₂-t₄, whereas the current I tends tozero. t₃ indicates the instant of time, when the switch 32 is closed. t₄indicates the instant of time, when the recovery of the energy from thewires 3,4 is finished. It is conceivable to predefine t₃ such that theswitch 32 is closed before or after t₄.

In FIG. 7 the dashed line 71′ in the time interval t₄-t₅ indicates thesituation, where there is still plasma surrounding the target 8. Byclosing the switch 32 at time t₃ the PFPN circuit 30 becomes active toshorten the time in which the arc is burning. Any electrons near thetarget 8 are caught, causing a current flowing through the PFPN circuit30 as indicated by arrows 83 in FIG. 10. Thereby, the plasma floatingpotential (potential to which the target 8 is charged due to the plasmaalone) decreases and the arc cannot be self-sustained anymore. Thediodes 31 and 45 act as selective switches: Since the currents 81 and 83are in opposite directions, the current 83 will flow through the closedswitch 32, as soon as the energy in the wires 3, 4 causing the current81 is fed back to the power supply circuit 10.

At time t₅ the switch 32 is opened. t₅ is chosen such that the arc isunlikely to reoccur.

At time t₆, which may be shortly after t₅, the switch 25 is closed whichhas the effect that the power of the power supply circuit 10 is suppliedagain to the electrodes 5 and 6. At the same time, the current 82circulating in the switch 22 will pass progressively through the plasma.The voltage U across the electrodes 5 and 6 goes back to a negativevalue, whereas the current I increases again (see time interval t₆-t₇ ofcurves 70 and 71 in FIG. 7).

At time t₇, the switch 22 is opened, such that the remaining current 82flowing through the switch 22 is forced to flow into the plasma, whichaccelerates the process of recovering the plasma. The voltage U changesfurther by an amount of U₂₂, which is the voltage across the switch 22at time t₇, whereas the current I increases further. If the switch 22 isa transistor which is apt to operated in the avalanche mode, it ispossible to dissipate the energy of this residual current 82, such thatnot all of this energy has to be absorbed by the plasma. (See FIG. 11,in which the switch 22 is indicated by the inherent avalanche diode ofthe MOSFET.) The provision of switch 22 has the advantage that a runawaycurrent can be prevented, i.e. a current which is accumulated duringsuccessive actuations of the switch 25 and which may have the effectthat the arcs get more and more energy.

The switch 22 is actuated such that it is closed when the switch 25 isopen, and open during a time interval which is long enough such that thecurrent 82 flowing through the freewheeling diode 23 of the switch 22has vanished.

At time t₈, the arc detection circuit 61 checks whether the conditionsfor an arc are still met. (This is not the case in the example shown inFIG. 7.)

At time t₉, the current flowing through the inductor 21 corresponds tothe current I passing through the plasma and the switch 22 may be closedagain.

At time t₉, the plasma processing is in the normal operation mode as itwas at time t₀.

In the following an example of detecting and quenching an arc and itstiming are discussed. The arc detection circuit 61 is designed such thatit generates an arc detection signal when at least one of the followingconditions is met (in the following denoted by “arc conditions”):

1. The current I in the plasma exceeds a certain value I1,

2. the absolute value of the voltage between the electrodes 5 and 6(denoted by |U|) drops by a certain amount U0 while at the same time thecurrent I in the plasma is above a certain minimum value I2,

3. the absolute value of the voltage |U| falls below a threshold U1while at the same time the current I is above a certain minimum valueI3.

In the present embodiment the minimum values I2 and I3 are set to beequal.

The controller 60 is adapted to receive various parameters for operatingthe power supply device which may be set by the user. Optionally, thecontroller 60 may be designed such that the operating parameters arevariable in time by using a self-adaptive process to set one or more ofthe operating parameters during operation. The operating parameterscomprises e.g. the voltage change U0 or the thresholds U1, I1 and I2 forarc detection, which are used by the arc detection circuit 61, and thevarious time intervals (delays) for controlling the switches 22, 25, 32and the bridge circuit 13. Examples of such delay parameters are:

D1: time interval during which the power supply device tries to quenchan arc before the bridge circuit 13 is switched off. Thus, D1 definesthe number of times the switch 25 is, in an event of an arc, actuatedbefore the power supply circuit 10 is switched off

D2: time interval during which the bridge circuit 13 is switched off

D3: time interval when the switch 25 is open. D3 corresponds to theinterval t₂-t₆ in the example of FIG. 7.

D4: time interval during which the arc conditions are to be met beforethe switch 25 is opened. D4 corresponds to the interval t₁-t₂ in theexample of FIG. 7.

D5: time interval between the closing of switch 25 and the checking stepwhether the plasma condition is met, i.e. whether the arc event is over.D5 corresponds to the interval t₆-t₈ in the example of FIG. 7.

As already mentioned above, the parameters may be variably set by aself-adaptive process. For example, the threshold U1 can be given by theaverage plasma voltage |U| plus a predefined valued. The delays D2 andD3 define the quenching time interval during which, in an event of anarc, no voltage is generated across the output terminals 1, 2.

The delay D3 may be set by means of the self-adaptive process such thatD3 is increased if the plasma does not recover after one cycle ofactuating the switches 22, 25, 32 to quench the arc.

FIG. 12 shows a first example of the temporal development of |U| (solidcurve) and I (dash-dotted curve). The example is similar to the exampleshown in FIG. 7. At time t₈, i.e. after one cycle of actuating theswitches 22, 25, 32, the voltage |U| is greater than U1 and the currentI is less than I1. The arc conditions are not met anymore. Thus, theplasma processing is in the normal operation mode again.

FIG. 13 shows a second example of the temporal development of |U| (solidcurve) and I (dash-dotted curve). In this example the delay D3 is set bymeans of a self-adaptive process. At time t₈, i.e. after one cycle ofactuating the switches 22, 25, 32, the voltage |U| is still less than U1and the current I is greater than I2. The arc conditions are still met.The delay D3 is increased. At time t₁₁, i.e. after the second cycle ofactuating the switches 22, 25, 32, the arc conditions are not metanymore and the plasma processing changes to the normal operation mode.

FIG. 14 shows a third example of the temporal development of |U| (solidcurve) and I (dash-dotted curve). In this example the arc conditions arestill met at time t₁₁, i.e. after two cycles of actuating the switches22, 25, 32. In this example the time interval D1 has expired, whichmeans that there is no other try to quench the arc. The power supplycircuit 10 is switched off by switching off the bridge circuit 13, suchthat no power is supplied to the terminals 16, 17 for the time delay D2.At time t₁₂ another cycle of actuating the switches 22, 25, 32 and thecircuit 10 is started to re-ignite the plasma. The successive switchingoff and on of the power supply circuit 10 and the switch 25 is indicatedin the lower diagram in FIG. 14.

The power supply device according to the invention is suitable for anyplasma processing operation, such as sputtering, PECVD (Plasma EnhancedChemical Vapour Deposition), etching, etc. The plasma processingoperation may include usual materials as well as materials which aredifficult to be processed such as zinc oxide (ZnO) or aluminum-dopedzinc oxide (AZO).

The power supply device according to the invention has the advantagethat when the power to the processing chamber is interrupted, lessenergy is involved in the arc occurrence. Thereby, the arc can bequenched quickly and the risk of damaging the target (and/or substratewhen present) is reduced. In addition, it has been found that possibleconsecutive arcs are suppressed in an efficient way, such that thenumber of arc events is reduced.

Although the present invention has been described in relation toparticular embodiments thereof, many other variations and modificationsand other uses will become apparent to those skilled in the art. It ispreferred, therefore, that the present invention be limited not by thespecific disclosure herein, but only by the appended claims.

What is claimed is:
 1. A power supply device for plasma processing,wherein electric arcs may occur, comprising, a power supply circuit forgenerating a voltage across output terminals, said output terminalsbeing for connection to a plasma processing chamber by means ofconductors, an interrupting switch connected between said power supplycircuit and one of said output terminals for interrupting the powersupply to said plasma processing chamber in case of the occurrence of anarc, and an energy recovery circuit connected to said output terminalsand to said power supply circuit, said energy recovery circuit servingfor feeding at least partially the energy which is stored in saidconductors when said interrupting switch is actuated to interrupt thepower supply to said plasma processing chamber back to said power supplycircuit; wherein said power supply circuit is configured to reuse theenergy fed back at least partially for the power supplied to said plasmaprocessing chamber.
 2. The power supply device according to claim 1,wherein said recovery energy circuit comprises a transformer or a DC-DCconverter or both.
 3. The power supply device according to claim 1,wherein said power supply circuit comprises a transformer having aprimary side and a secondary side, the connection of said recoveryenergy circuit to said power supply circuit being arranged at saidprimary side of said transformer and the connection of said recoveryenergy circuit to said output terminals being arranged at said secondaryside of said transformer.
 4. The power supply device according to claim1, wherein said power supply circuit comprises a capacitor connected tosaid recovery energy circuit for storing at least partially said energyfed back.
 5. The power supply device according to claim 1, wherein saidinterrupting switch is an IGBT, a power MOSFET, or another kind oftransistor.
 6. The power supply device according to claim 1, furthercomprising an arc detection circuit for detecting arc events in saidplasma processing chamber, said arc detection circuit being configuredto determine at least one of the following criteria defining an arcevent: the current I through electrodes, between which the plasma isgenerated, exceeds a given value I1, the absolute value of the voltage,|U|, across said electrodes drops by a given amount U0, while saidcurrent I is above a given minimum value I2, |U| falls below a thresholdU1 while said current I is above a given minimum value I3.
 7. The powersupply device according to claim 1, further comprising a floatingpotential neutralizing circuit connected to said output terminals forreducing the floating potential which is produced on at least one of atarget and a substrate located in said plasma processing chamber aftersaid interrupting switch is actuated to interrupt the power supply tosaid plasma processing chamber.
 8. The power supply device according toclaim 7, wherein said floating potential neutralizing circuit comprisesa switch connected to said output terminals.
 9. The power supply deviceaccording to claim 1, wherein said power supply circuit is designed togenerate a continuous DC voltage or a pulsed DC voltage across saidoutput terminals.
 10. The power supply device according to claim 1,further comprising an inductance circuit which is arranged between saidpower supply circuit and one of said output terminals and whichcomprises an inductor and a second switch, wherein said interruptingswitch is arranged outside of said inductance circuit and wherein saidsecond switch is connected parallel to said inductor.
 11. The powersupply device according to claim 1, further comprising a controller forcausing said power supply circuit and said interrupting switch to beswitched on and off, said controller being configured to determine aquenching time interval by means of a self-adaptive process, thequenching time interval defining the time interval during which, in anevent of an arc, no voltage is generated across said output terminals.